1. Field of the Invention
This invention relates to a fire-resisting mine sealant made of a polyurethane foam containing a large loading of an inorganic material such as aluminum hydrate, a phosphorous compound and having a small amount of a char enhancer present. By spray coating the interior surface of a mine, such as the shafts, entries or tunnels, with this polyurethane foam forming material, a foam coating is formed which seals these interior surfaces against the effects of air and moisture on the rock. In addition, the coating layer reduces the tendency for the rock to weaken and fall to the ground and, more importantly, the coating resists burning as measured by burning tests. These tests, however, are not intended to reflect hazards presented by this or any other material under actual fire conditions.
2. Description of the Prior Art
In the 1950's and 1960's polyurethane foams were used as mine sealants. See "Rigid Foams for Mines", by Donald W. Mitchell et al, U.S. Dept. of the Interior, Bureau of Mines 1964. However, as a result of disastrous fires in mine tunnels, where these foams rapidly burned and produced a hazard to miners, they are not now generally used to provide a uniform mine sealant coating throughout the mine. See, for example, "Fire Hazards of Urethane Foam in Mines", by Donald W. Mitchell et al, U.S. Dept. of the Interior, Bureau of Mines 1966.
Instead, other fire-resistant materials have been employed, such as cement coatings. While these materials are commercially sold and used, they are not flexible coatings. It would be advantageous to have a polyurethane type of foam that could be easily sprayed in place and which would not only fill in all of the cracks and crevices, but also maintain the coating intact even when the mine surfaces shift slightly over a period of time.
3. Objects of the Invention
It is an object of the present invention to provide mine sealant coatings which are more fire resisting than polyurethane foams by utilizing special polyurethane foam-producing reactants which permit the incorporation of large quantities of selective additives to provide fire retardancy.
It is a further object of the invention to provide a flexible polyurethane foam coating to be used as a mine sealant which is able to accomodate shifts in the earth's structure over time so as to maintain a satisfactory coating on the exposed surfaces in the interior of the mine to reduce the tendency of the rock to weaken and fall.
It is also an object of the invention to provide a foam coating to seal the surfaces of mine shafts, entries or tunnels which is easy to apply by spraying. A spray gun can mix a prepolymer supplied under pressure from one source with a water phase containing at least some of the additives applied from a second source.
It is also an object of this invention to spray onto a substrate a fire-resisting polyurethane foam having a large inorganic content to provide insulation for use in buildings and for other insulating purposes.
These and other uses will become evident from the following detailed disclosure.